The present invention relates generally to a system for transmitting compress-encoded image data, and more particularly to an image data transmission method which reduces a delay due to compress encoding.
Systems which compress encode image data and transmit the encoded data through a network have been brought into practice such as a television telephone system, a teleconference system, a monitoring system, and so on. Such systems employ encoding schemes such as ITU-T, H.261, MPEG (Moving Picture Experts Group), or the like to enable highly defined image information to be transmitted within a narrower transmission bandwidth.
In a system which utilizes inter-frame information to compress image data as does MPEG, and transmits the compressed image data, a transmission delay generally occurs during the compression processing on the order of 150 to 500 ms except for a delay on the network.
Thus, the above-mentioned system has a problem in that, for example, when a mechanical system is controlled to perform panning/tilting, zooming, focusing and so on of a television camera on the transmission side of image data while produced image data is being viewed on a monitor on the reception side, a longer delay time intervenes until an image is displayed on the monitor in response to an inputted control instruction. Particularly, since the control of the television camera for panning/tilting involves controlling the rotation of a rotating pedestal, this exaggerates the problem of long delay time.
In a system which transmits a plurality of pictures as one GOP (Group of Pictures) like MPEG, on the other hand, when a stream of image data is switched among a plurality of image sources, a problem exists in that a switching delay occurs for a time period corresponding to the number of pictures comprising the GOP at maximum.
The present invention has been made to solve the problems as mentioned above, and it is an object of the present invention to provide an image data transmission method which is capable of reducing a delay associated with the compression processing of image data.
It is another object of the present invention to provide an image data transmission method which is capable of reducing a switching delay possibly caused by switching streams of image data having the GOP structure.
An image data transmission method according to one aspect of the present invention is applied for use with an image data transmission system which comprises a plurality of image data transmission apparatus for compress encoding image data and transmitting compress-encoded image data, an image data reception apparatus for receiving the image data, control device for controlling the image data transmission apparatus, and a network for interconnecting the respective apparatuses. When the image data transmission apparatus is controlled by the control device, the control device acquires information on capabilities of the plurality of image data transmission apparatuses. When the control device determines based on the information on capabilities that a controlled image data transmission apparatus has a function which is affected by a delay due to the compress encoding, or when the controlled image data transmission apparatus uses a function which is affected by the delay due to the compress encoding from among the functions, the image data transmission apparatus is controlled to perform compress encoding that reduces the delay. With this configuration, when the image data transmission apparatus is controlled to operate mechanical systems, for example, while viewing a monitor of the image data reception apparatus, it is possible to reduce a delay time which intervenes until an image responsive to an inputted control instruction is displayed on the monitor.
Also, an image data transmission method according to another aspect of the present invention is applied for use with an image data transmission system which comprises a plurality of image data transmission apparatuses for converting image data to a compress encoded stream having a GOP structure and transmitting the compress-encoded stream, an image data reception apparatus for receiving the stream, a selector for selecting one from the image data transmission apparatus, and a network for interconnecting the respective apparatuses. When the selector switches from an arbitrary image data transmission apparatus to another image data transmission apparatus, the GOP structure is changed for a predetermined time period immediately after the switching to reduce a delay caused by the switching. With this configuration, it is possible to reduce a switching delay time which may occur when a plurality of image data streams are switched among the image data transmission apparatuses.